Aminophenols are very useful compounds from an industrial point of view, which have heretofore been widely used as intermediates to medicines, agricultural chemicals, azo dyes, anti-oxidants, photographic developers, etc. and also have recently come to be used as starting materials for heat resistant resins such as polyimides or polyamides. While the process for the production of an aminophenol by reacting a divalent phenol and ammonia in the absence or presence of a catalyst is known, the reaction mixture thus obtained contained considerable amounts of the unreacted divalent phenol and by-products in addition to the end product aminophenol. Without efficiently separating these compounds, especially when the use in medicines, agricultural chemicals, etc. was contemplated, the presence of these impurities greatly hampered the successful production of high-quality medicines, agricultural chemicals, etc. Therefore, special purification steps have heretofore been necessary.
In order to obtain a purified aminophenol by separating the aminophenol from the unreacted divalent phenol and/or by-products from the reaction mixture, several methods have been proposed, for example:
(i) Japanese Patent Application (OPI) No. 28429/1973 describes a method which comprises the liquid-liquid extraction of crude aminophenol obtained by the reaction of a divalent phenol and ammonia in the absence of a catalyst, using a water-diisopropyl ether solvent. (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".) PA0 (ii) British Pat. No. 1,228,568 describes a method which comprises contacting crude p-aminophenol with a liquid aliphatic, alicyclic or aromatic ketone. PA0 (iii) British Pat. No. 1,028,078 describes a method which comprises washing crude p-aminophenol obtained by the catalytic hydrogenation of nitrobenzene under acidic conditions, using an aliphatic alcohol, preferably isopropanol. PA0 (iv) British Pat. No. 1,324,787 describes a method which comprises the liquid-liquid extraction of crude p-aminophenol with a solvent of benzene, toluene, xylene or an acetic acid ester and water. PA0 (v) British Pat. No. 1,291,642 describes a method which comprises the liquid-liquid extraction of crude p-aminophenol with a solvent of carbon tetrachloride, 1,1,1-trichloroethane or 1,1-dichloroethane and water. PA0 (vi) Japanese Patent Application (OPI) No. 69543/1980 describes a method which comprises the extraction by contacting crude p-aminophenol aqueous solution with an aromatic amine.
Then, the present inventors replicated these spreading and purifying methods and consequently found that although there was exerted a reasonable purifying effect by either method, the separation of the aminophenol from the divalent phenol and/or by-products was still inadequate and, in addition, the methods (i) to (vi) were unsatisfactory also in an aspect of the yield. In other words, in the above-described method (i), since the solubilities of both the aminophenol and divalent phenol in water are great, the separating efficiency between the aminophenol and divalent phenol is poor, and further, the loss of the aminophenol is brought about to decrease the yield, and therefore, it was economically disadvantageous. Further, since the above-described methods (ii) to (vi) are basically intended to be applied to p-aminophenol obtained by the catalytic hydrogenation of nitrobenzene under acidic conditions and hence, the by-products thereof are inherently different from those in the case of the aminophenol obtained by the reaction of the divalent phenol and ammonia, the separation of the aminophenol from the unreacted divalent phenol and/or by-products was difficult.
Therefore, the present inventors have been intensively studying on a method for its separation and purification free from the above-described drawbacks, and, as a result, have discovered that the aforesaid object may be achieved by reacting a divalent phenol and ammonia in the absence of a catalyst or in the presence of a water-soluble catalyst to obtain a reaction mixture, obtaining a separated and recovered product containing an aminophenol and the unreacted divalent phenol from the reaction mixture, contacting this separated and recovered product with an aliphatic ether substantially incompatible with the aminophenol in an inert gas atmosphere at a temperature at which the separated and recovered product melts or higher, then cooling to induce the crystallization of the aminophenol, filtering to obtain a cake mainly composed of the aminophenol, further melting and contacting this cake with an aliphatic ether in the co-presence of water and a surfactant in an inert gas atmosphere, and then cooling thereby inducing the crystallization of the aminophenol and recovering it, and thus have accomplished this invention. By this invention, it is possible to efficiently separate the aminophenol from the unreacted divalent phenol and/or by-products from the reaction mixture and moreover, the aminophenol obtained by such separation is of a high quality.